The present invention relates to a head drum construction for use in a magnetic tape recording and reproducing apparatus such as VTR apparatus.
Some magnetic tape recording and reproducing apparatus such as VTR apparatus have a recording video head and a playback monitoring video head which are combined in a single head drum construction. The playback monitoring video head serves to reproduce, with a short time delay, signals recorded on a magnetic tape by the recording video head in order that the user can record video information while confirming proper recording operation. The level of signals processed by the recording video head is more than ten thousand times that of signals that the playback monitoring head processes. Therefore, there is a strong tendency for such a head drum construction to suffer from crosstalk due to electromagnetic coupling of energy from the recording head to the monitoring head. No mechanical means have been incorporated in the prior head drum for preventing such an unwanted signal interference from occurring. It would be possible to insert an amplifier in a playback signal transmission system for electrically suppressing crosstalk by reducing the difference between the signal levels. However, incorporating such an additional electric circuit would render VTR apparatus complicated in structure, result in a reduced rate of production of VTR apparatus and make the repairing thereof difficult. The cost of manufacture of VTR apparatus with such amplifiers would be so prohibitive that they could not be mass-produced. The conventional head drum constructions have had no effective means for reducing the undesirable crosstalk to allow good playback monitoring.